This Thai-US collaborative application seeks to develop and conduct a non-randomized effectiveness and cost-effectiveness study of a multi-level combination HIV preventive intervention with and without daily oral Tenofovir/Emtricitabine (Truvada) pre-exposure prophylaxis (PrEP) with mobile phone-based SMS adherence support among young men who have sex with men (YMSM) in Bangkok, Thailand. The current epidemic of HIV among Thai YMSM (men aged 18-26) is marked by high HIV incidence (5-12/100py) despite current prevention and treatment efforts, and rates are highest among the youngest men, aged 18-21, and among the subset of YMSM who sell sex. The proposed combination intervention will include individual level components: frequent HIV testing, risk reduction counseling, condom and lubricant distribution, and behavior change counseling; community awareness and mobilization; and an open label offer of PrEP with SMS (FrontlineSMS) adherence support. Participants will include Thai YMSM engaged in sex work or with a history of recent (in the previous 12 months) selling sex. The proposed study will be conducted by Johns Hopkins, Mahidol, and Emory Universities; The Thai MOPH-US CDC Collaboration (TUC) and its Silom Community Clinic @ Trop Med (SCC); and community partners including SWING, a sex worker empowerment and health promotion group; Rainbow Sky, an LGBT health and rights group; and APCOM, the Asia-Pacific Community of MSM. This group combines unique expertise, access, and experience in working with YMSM in this hyper-epidemic context. The study will include a formative phase using qualitative and community engagement methods to refine the intervention; a pilot; the open label intervention assessing effectiveness of combination interventions with and without PrEP and SMS adherence support with an HIV infection endpoint; and a costing and cost-effectiveness assessment which will measure the costs associated with the combined intervention, the number of infections averted through PrEP use, discounted treatment costs save, and assess whether the intervention packages are cost- saving, cost effective, or not cost-effective. The effectiveness study has been powered on the comparison of person time on PrEP versus not on PrEP and will employ propensity score methods to reduce the potential bias inherent in the self-selection design. In all the study proposes to enroll 1240 YMSM, 620 who choose PrEP and 620 who do not choose PrEP.